Sue Griffin, PhD Dillard Professor and Vice Chair Donald W. Reynolds Department of Geriatrics

1. The Genetics Of Alzheimer’s Sue Griffin, PhD Dillard Professor and Vice Chair Donald W. Reynolds Department of Geriatrics University of Arkansas For Medical Sciences Research Director GRECC VAMC Little Rock, Arkansas

3. Genes are on chromosomes present in the nucleus of every cell

4. The genetic code has four letters: A=adenine, T=thymine, G=guanine, C=cytosine

5. Chromosomes in the nucleus The yellow ribbon is held together by A—T and C—G

6. Chromosomal DNA (genes) carry the code for all proteins necessary to make our body

7. Facts: • A complementary strand (messenger RNA) is made to nuclear DNA—an A on the mRNA is paired with a T on the gene and C with G, over and over to code for the building blocks (amino acids) needed to make every protein! • Every amino acid has a unique code

9. Diversity of Genetic Diseases Simplistic: • One gene mutation causes every case. More Complex: • Multiple gene mutations cause all cases. Most Complex: • Multiple gene mutations cause some cases. • Multiple polymorphisms increase risk. • Multiple environmental factors increase risk.

10. What Starts Everything Going Wrong In Alzheimer’s Disease? • The genes you inherit (nature) • Wear and tear of time (aging) • The way you handle • your inheritance (nurture)

11. When You’re Old but Okay

12. Nerve Cells and How They Work In Normal Brain • The nucleus • The cytoplasm • The processes • The transmission • of information

13. When your brain is hot and fine

14. Progression from Hearing to Speaking and from Reading to Mulling It All Over

15. Affected Regions at Different Stages of Alzheimer’s Disease MODERATE MILD SEVERE

16. When the Brain “Cools Down” Alzheimer’s disease Clincally Normal

17. The Problem in Alzheimer’s Disease fromOne of His Own Cases MB Graeber 1997 Neurogenetics

18. Plaques in Alzheimer Brain 10 µm Aβ plaques,activated glia,neuronal DNA

19. What is that sticky insoluble stuff in plaques? • The b-pleated sheet protein b-amyloid (Ab) • George Glenner sequenced the proteinand Konrad Beyreuther, Dmitry Goldgaber, and St. George-Hyslop and colleagues mapped the Ab precursor protein (bAPP) gene to chromosome 21 • This is important!!

20. bAPP is Cleaved to Form b-amyloid Functions of bAPP • Responds to injury • Membrane Functions • Interacts with PS1

21. Reasoning Behind This Discovery? Fact: • People with Trisomy 21 have Alzheimer Ab • plaque pathology by middle age (Wisniewski, 1989) Hypothesis: • Plaques in Down’s as in Alzheimer’s are the product of APP cleavage, so it’s logical that mutations in bAPP cause the disease in families with lots of Alzheimer’s. Tanzi and others took this candidate gene approach (Plan A in genetic studies).

22. Plan A - Sequence a Specific Gene Studies of Alzheimer families that were based on a pathological characteristic of the disease • Because Ab plaques were the most prominent neuropathological feature, bAPP was the targeted gene in AD in these families. • At least three offending bAPP mutations in DNA from family members have been identified by searching for mutations by mapping of this gene.

23. bAPP Mutations Cause Alzheimer’s Disease . . How did we come to know this??

24. We thought that we were nearly there! The cause! Yes! But that was only 1989 and . . .

25. Family Association Studies • Then they asked: Do all family members with the mutation have the disease? Yes • Do family members who don’t have the mutation have the disease? No (Maybe?) If yes on the first and no on the second = Disease associated, Causative, and Dominant!

26. Hmm ~ Why Maybe Not all familial Alzheimer’s disease families have mutations in this gene And all of the known bAPP mutations taken together don’t account for all of the people (>5%) with familial Alzheimer’s

27. So Plan B - Mapping Studies -Identified Two Other Causative Genes • Taking a more unbiased approach—that is, not looking for a missense sequence in a specific protein—researchers used endonucleases to cleave DNA for restriction fragment length polymorphism (RFLP) studies to identify aberrant cleavage sites. This type of chromosome mapping, identified two more mutated genes (Presenilin-1 and -2) that, like bAPP mutations, are causative for Alzheimer’s disease.

28. Notes on RFLP Studies • Restriction endonucleases are enzymes that cleave DNA at specific sites. • Absence of a cleavage site can be used to identify a missense or mutated site

29. Plan B Also Identified one of three Apolipoprotein E polymorphisms (e 4) Associated with Increased Alzheimer Risk • RFLP mapping of DNA from a case control study identified a chromosome 19 region that associated with, but not causative of, Alzheimer’s disease. The variant was ApoE e4.

30. Mutations: Several in the APP Gene Presenilin 1 and 2 Genes Copy Number: APP e.g. Down’s syndrome Polymorphisms: Apolipoprotein E Genes Inflammatory Genes

31. ApoE Facts • ApoE is important in transport of lipoproteins. But its specific role in neurons is unknown. • There are three variants—e2, e3, and e4. • The ApoE ε4gene carries a high relative risk: • Inheritance of e4 increases Alzheimer risk 3-9X. • More than half of Alzheimer patients have one or more e4 alleles. • Inheritance of the e2 allele may be protective.

32. Some ApoE 2, 3, and 4 Facts These isoforms differ from each other only by single amino acid substitutions at positions 112 and 158 of the 299 amino acid protein but have profound physiological consequences. E2 is uncommon but is associated with both increased and decreased risk for atherosclerosis. Approximately 64 percent of the population carries one or two E3 genes. E3 is the "neutral" Apo E genotype. E4 has been implicated in athero-sclerosis and Alzheimer's disease, impaired cognitive function, and reduced neurite outgrowth.ApoE is a target gene of liver X receptor, a nuclear receptor member that plays a role in metabolic regulation of cholesterol, fatty acid, and glucose homeostasis. Look in Wikipedia

33. bAPP is Cleaved to Form b-amyloid Functions of bAPP: • Expression increases • in response to injury • and in aging • Membrane Functions • Interacts with PS1

34. ApoE Regulates APP Expression Neurons In Culture ApoE3 ApoE4 Alzheimer Brain

35. Plaque proximity = less neuronal APP AbbAPPNuclei

36. One Important Driver A neuroinflammatory Cytokine named interleukin-1 (IL-1). Why would I say that? What can IL-1 drive?

37. What Does IL-1 Do? • To Neurons • Increases production of: • i) bAPP • ii) Faulty tau (hyperphosphorylated) • iii) Enzymes that breakdown • neurotransmitters • Decreases production of: • i) synaptophysin

38. Neuro-fibrillary Tangles (red) IL-1 in Microglia (green)

39. Interleukin-1 has a Sister Cytokine ~ TNFa • TNF and IL-1 are both elevated • in Alzheimer’s disease. • 2. They induce each other and act • as neuroinflammagens. • 3. Both act as gliotransmitters.

40. Yes Are their heritable variants of the genes that encode these drivers that might increase risk for Alzheimer’s disease? Probably

41. Factor Odds Ratio ApoEe4 5.5 IL-1A 2,2 4.9 IL-1 Genotype and Age at Alzheimer’s Onset Grimaldi, Griffin, et al. Ann Neurol, 2000

42. Confirmation of an Old Idea • Breitner JC et al Neurology 1994;44:227 • 2. in ’t Veld BA et al Neurobiol Aging 1998;19:607 • 3. Zandi PP et al Neurology 2000;54:2066 • 4. Vlad SC et al Neurology 2008;70:1672 • 5. Szekely, C. A. Neurology 2008;70:17

43. Adjusted odds ratios of Alzheimer’s for ibuprofen ( ) and naproxen () X O

44. Combat Strategies • Prevention: • Exercise • Diet and Stop Smoking • Combat Inflammation • Treatment: • Education and Cognitive Reserve • Meds: Aricept, Namenda

45. We are our genes

46. But we get to decide what we do about our genetics!